Influence of short-term heat treatment on the second-order curing epoxy tack coat in steel deck pavements

Abstract

Second-order curing epoxy tack coat (SCETC) is widely used as a waterproof bonding layer on epoxy steel bridge deck because it solves the problems of inadequate bonding and damage caused by the construction machine at the same time. In this paper, simulated short-term heat treatment (SHT) was carried out on SCETC after first-order curing. The reaction process and microstructure evolution of SCETC before and after SHT were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, and polarized light microscopy. The influence of SHT on mechanical properties of SCETC was comprehensively analyzed through tensile test, pull-off test, bonding behavior test and shear resistance test. The SCETC reaction process before and after SHT was revealed for the first time in this paper. At room temperature, amine curing agent (ACA) reacts with epoxy groups, and latent curing agent (LCA) dissolved in ACA gradually seeded out as fibrous crystals. Under the action of the high temperature of hot mixture, the LCA crystals melts and further reacts with the residual epoxy groups. When the melt volume-flow rate (MFR), tensile and pull-off properties of SCETC were compared before and after SHT, the two-stage curing mechanism of SCETC was further deduced. The fibrous LCA crystals seeded out during first-stage curing can enhance the solidified material. The LCA crystal melts under SHT, and its strengthening effect on the solidified material weakens or even disappears. Based on the unique reaction process of SCETC, the effective bonding time of SCETC under different curing conditions can be further determined by testing the bond performance between steel and epoxy asphalt concrete (EAC), and provide guidance for field construction. The effective bonding time of SCETC are 24 h at 60 °C, 48 h at 40 °C and>72 h at 23 °C, respectively.